Apparatus for neutralizing radiointerference on wire lines



June 30,' 1925.

R. N. HUNTER APPARATUS FOR NEUTRALIZVING RADIOI'NTERFERENCE ON WIRE LINES' Filed Novjzo, 1922 www @.www

INVENTOR. W/f

. Q ATTORNEY v Patented `lune 30,` 1925'.

UNITED STATES PATENT OFFICE.

RUSSELL N. HUNTER, 'or BROOKLYN, NEW YORK, AssIGNOR'rO AMERICAN TELE- rHONE AND TELEGRAPH COMPANY, A CORPORATION or NEW YORK.

APPARATUS FOR NEUTRALIZING RADIOITlilffFllIRJIlIl'IlEy ON WIRE LINES.

Application led November 20, 1922.* Serial No. 602,145.

- To all whom t may concern:

Be it known that I, RUSSELL N. HUNTER,

residing at Brooklyn, in the county of Kings and State of New York, have invented certain Improvements in Apparatus for Neutralizing Radiointerference on Wire Lines, of which the following is a specification. L

This invention relates to transmission cirlcuits, and more particularly to a newv and 'improved system for overcoming interference Onsignaling conductors due to fradio transmission. y

In carrier transmission systems in which carrier channels are superposled on ordinary signaling conductors,interference is sometimes produced in one or more of the carrier channels due to radio signals transmitted at the, carrier frequency assigned to the channel. 'In order to overcome this difiiculty, it has heretofore been proposed to balance. out the interfering frequency by impressing upon the channel a balancing frequency of equal amplitude and opposite phase, the balancing frequency being obtained from the disturbing source through the medium of an' auxiliary circuit which is subject to the disturbing influence.

In applying this remedy, some difficulty has been experienced in obtaining the proper balance due to the fact that adjustments of the balancing potential must be made both with respect to phase and amplitude, and instrumentalities ,heretofore used for -obtaining such adjustments have been of such a 4character, that an adjustment of either the phase' or the amplitude results in a change in the other, so that it has required considerable manipulation in order to obtain a balance. It is one .of the objectsof the present invention to provide a system in which the phase and amplitude of the balancing potential may be controlled each independently of the other, so that A or vice versa.

when the phase angle -has once been adjusted, changesin amplitude may thereafter be made without changing the phase angle,

The arrangements whereby these results are accomplished may be understood from the following description of the invention when read in connection with-the accompanying drawing, Fig. l'ofwhich illustrates a circuit arrangement for neutralizing radio interference in a carrier system involving a high-pass filter for obtaining a phase -adjustment independent of the amplitude adjustmcnt.

Fig. 2 shows a similar circuit arrangement -employing a low-pass type of filter /for obtaining the phase adjustment.

' Figs.l 3 and 4 graphically represent the HFL terminates at a carrier station intwo branches, a low frequency branch LFL connected to the carrier line through the low pass filter LP, and a carrier branch X associatedwith the high` frequency line HFL through a high-pass lter HP. Associated with the carrier branch X will be transmitting land receiving apparatus for a plurality of channels having different frequencies, but as this apparatus is .not concerned with the present invention the idetails thereof ,need not be disclosed.

A high frequency carrier line, sucgh as HFL, is subject to interference fromv radio transmitting stations, and the interfering currents, if they happen to fall within the range of One'of the receiving channels, will,

,of course, produce disturbing signals in the receiving apparatus of such a channel.` In Order to overcome this difficulty, it is proposed by the present invention to superpose on the carrier branch X electromotive forces equal in amplitude but opposite in phase to the disturbing 'electromotive forces. For this purposean antenna system A is provided for receivin electromotive forces from the distant radlo station producing the interference. A circuit 20 associates the antenna A with thecarrier branch X through a balanced transformer 21- so4 arranged that' a high-pass filter is substantially non-Jating out other frequencies than vthe particular frequency which it is desired to use for neutralizing purposes.

A single section of a high-pass filter 22 is.

vincluded in 'the circuit 20 for producing capacities C.v By adjusting the values of the capacities alone or making suitable adjustments of both the capacities and the inductance, phase adjustments may be made without producing any change in amplitude. While this result may appearto be somewhat unusual, when it is remembered that tenuating with respect to frequencies lying wit-hinl its range, the reasonfor the result becomes more apparent.

In making phase adjustments by mean ofthe high-pass lter 22, the' inductance and capacity'elements will be varied in steps, but thetwo condensers should be kept equal to each other. lThe relation between the in du'ctance and capacity is given by the L* 20.202 (l) n in which fw crepresents 21: timesrthe fre-v quency. The relation of this formula is derived on the assumption that, when one side of the network is terminated in a resistance of R ohms, the impedance, looking into the other side ofthe network, will also be R ohms non-inductive. The phase change due to the network is given by the formula;

' R j gup=tan 1 Lwlm (2).'

w Curves computed in accordance with formulae 1 and 2 are illustrated in Fig.`3, for the case in which the'frequency whose phase angle is to be changed is 19,000. cycles, and the impedance of the circuit looking into the transformer 21 from the filter is adjustment of the capacity .600 ohms. In Eig..3, the curve designated L 1s a plot showing the value of the inductance corresponding 'to each capacity setting of the capacity C ofthe filter 22. o The curve marked qs shows the phase change for each C the inductance dingly adjusted. It will be seen that by varying the,v capacityl from .002 microfarads to .02 microfarads the lnductance L will be adjusted from about .018L henrys to about .005- henrys, and a phase change of about 90 will be obtained. The amount of this phase change may be 1 capacit-y.

increased as indicated by the ,curves by,

further increasing and further reducing the Thisv may not be practical, owever, as further increase in the capacity does not tend to produce a corresponding change in phase, while the smaller values of the capacity involve very sudden increases in the amount of inductance. -Consequently, where phase changes materially greater than 90 are desired, it may be necessary to use two filter sections in series to obtain the desired phase change.

It will also be noticed in the curve L of Fig. 3 the value of the inductance does not change materially over a very considerable variation in the values of the capacity of the filter, the curveL being almost flat through a large part of its range. This at once suggests that the network may be simplified by maintaining the inductance constant and only adjusting the two capacities. The curves of Fig. 4 illustrate the characteristics of the filter section as a phase adjusting device for .a frequency of 18,750 cycles with a terminal impedance of 600 ohms 4and a non-adjustable shunt inductance of .006 henrys.

The curve marked qb indicates the phase change corresponding to different 'values of capacity. The curve marked p represents the variation in ratio of the current flowing into the 600 ohm impedance with the filter in circuit to the current which would fiow into the impedance with the filter removed. Obviously, if the filter introduced no attenuation at. the frequency under consideration,

this ratio would be unity. Anexamination of the curve p shows that for a capacity range from about .0055 microfarads to somewhere over .03 microfarads this ratio does not depart excessively from unity, and consequently the phase adjustment` over this range may be obtained without material change in amplitude of the current. 'Y The phase change corresponding to this change incapacity runs from approximatel 35 to approximately 125, a total hase c an e of about90. It is not practica to make a justments outside of the range indicated, for an increase in the capacity does not roduce any substantial phase change, whi e a decrease in the capacity below the value .0055 produces avery marked increase in attenuation and also results in. a very sharp increase in the impedance of the filter, as indicated by the dotted line curve Z. Where phase changes greater than 90 are desired, it is best that two-filter 'sections in series should be used, so that the first section will shift the phase 90, andthe second section,-

lla';

Fig. 2 illustrates a' modified circuit in which a low pass filter section 22" is used as a' phase changing element. The other vfeathe midpoints of two half section induc` tances L. The inductances should be kept equal to each other, and the relation between inductance and capacity for `different adjustmen'tsv of the filter is gvien by the formula f 2L miiz (3) The phase change due to they network is given by the formula:

The characteristics of this type 4of filter as a phase changing device ale shown by the -curves of Fig. 5 for the case of a frequencyA of 18,7 cycles and a terminal impedance of 600 ohms. In Fig. 5 the curve L gives the values of inductance corresponding to different values of the capacity, while the 4curve marked indicates the phase change corresponding to each capacity value. The type vof filter employedv in Fig. 2 involves only one variable condenser, instead of the two necessary for the high-pass type o f Fig. 1,but in this case a fixedfinductance cannot be lused as the inductance varies materially for each material change in capacity,`as inl dicated by the lcurve L. There` is no part of the cnrve in which the linductance stays y reasonably constant over a range of capac` ity changes. This type of filter, however,

has the advantage t atjfaA greater phase change isobtained With-a single-section of the filter, so that in most cases it would not be necessary to use two sections. .For example, if the inductance be varied from zero to .O14 henrys, a phase change from zero to 140 will be obtained. The capacity will bev varied from zero to a maximum ofslightly over. .014 microfarads, and from this maximum point the capacity values fall 0H with further increase in inductance to a value of about .009 microfarads.

If desired the inductances L in the filter section 22 o f Fig. 2 ma be so wound as to have a certain amount o /mutual inductance.

this however, as a greater phase change .per In general, no/ advantage vwill be gained' by section is possible when the mutual inductance is z ero.

In thearrangements of both, of Figs. 1

l' and 2 the filter sections may be adjusted to produce -the'desired phase angle for the -b'alaclng component without producing 1 any material change in the amplitude of thecurrent, as the filter section is approximately non-attenuating. Adjustments in amplitude may be made' by a sim-` ple series adjustable resistance R1 included and amplitude of tlie current may be independently adjusted.

It willbe obvious that the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated without departing from the spirit of the invention as'defined in the following claims.

AWhat is claimed is:

1. In a wire signaling system subject to interference due to radio signaling, an auxiliary circuit upon which a similar disturbing-electromotive force may be impressed for balancing purposes, a device associated with Asaid auxiliary circuit for adjusting the phase of the current resulting from said balancing electromotive force and a device associated with said auxiliary circuitu for adjusting the amplitude of said current, said phase adjusting device and amplitude adjusting device controlling their respective functions independently of each other, said phase adjusting device having substantially no attenuation at theinterfering frequency.

2,. ln a wire signaling system subject to interference due to radio signaling, an aux* iliary circuit upon which a similar disturbing electromotive force may be impressed forbalancing purposes, a device associatedwith said auxiliary circuit for adjusting the phase of the current'resulting from said balancingelectromotive force and a device associated with said auxiliary circuit for adjustin the amplitude of said. current, said f the interfering frequency.

3. In a wire signaling system subject to interference due to radio signaling, anl auxiliary circuit upon which a similar disturbing electromotive forge may be impressed for balancing purposes, a device associated.

with said auxiliary circuit for-adjusting the phase ofV the current resulting from said balancing electromotive force and a device associated with said auxiliary. circuit' for adjusting the amplitude of said current, said phase 'adjusting device and amplitude adjusting device controlling their respective y functions independently of each other, and said phase adjusting device having substantially no .attenuation at Ithe interfering frequency, and Said phase adjusting device comprising a filter section "having series and shunt impedances, one of' said impedanees being inductive and the other capacitative, and said impedancel elements being so proportioned that the attenuation of the section is substantially zero at the interfering frequency.

4:. .The method of changing thel phase shift of a filter section having series and shunt impedance elements, which consists in so varying the absolute values of said elements as to produce a desired phase shift at a given frequency and so varying the relative values of the series and shunt elements as to produce substantially no change in impedance at the given frequency.

5. The method of changing the phase shift of a filter section having series and shunt impedance elements7 which consists in so varying the absolute values of s aid elements as to produce a desired phase shift at a given frequency and so varying the relative values of the series and shunt elements as to maintain tlie` attenuation at a substantially negligible vaille .for the desired frequency.

6. The method of changing the phase shift of a filter section having series and shunt impedance elements, which consists in so varying the absolute values of said elements as to'produce a desired phase shift at a given frequency and so varying the relative values of the series and shunt elements as to produce substantially no change in impedance and maintain the attenuation at a substantially negligible value for the desired frequency.

`7. The method of changing the phase shift of a filter section having series and shunt impedanceelementa one of which is lnductive and the other capacitative, which conslsts 1n so varying the absolute velues of 7the inductance and capacityjof said elements /the inductance and capacitv of said elements as to produce a desired phase shift at a given frequency and so varying the relative values of the inductance and capacity as to maintain the attenuation at. a substantially negligible value for the given frequency.

9. 'lhe method of changing the phase shift of a filter section having series and shunt impedance elements, one of which is inductive and the other capacit-ative, which consists in so varying the-absolute values of the inductance and capacity of said elements as to produce adesire-d phase shift at a given frequency and so varying the relative values of the inductance and capacity as 4to produce substantially no change in the impedance while maintaining the attenuation at substantially negligible value for the given frequency.

In testimony' whereof, I have signed my name to this specification this 18th day of November, 1922.

RUSSELL N. HUNTER. 

